Adaptive Synchronous Rectifier (SR) Controller

The NEX81801DA and NEX81802DA (NEX81801/2DA) are high performance synchronous rectification controllers used in switching mode power supplies. It supports operation in Discontinuous Conduction Mode (DCM), Continuous Conduction Mode (CCM) and quasi-resonant flyback converters.

The NEX81801/2DA regulates the forward drop voltage of an external synchronous rectifier (SR) MOSFET in two stages. This allows the SR FET to turn off quickly when the VDS becomes positive.

The externally adjustable turn-on blanking time can effectively prevent the synchronous rectifier from being falsely turned off due to leakage inductance and parasitic parameter oscillation.

The adaptive turn-on detection circuit can prevent the SR from being mistakenly turned on when the VDS DCM oscillation crosses zero during some load conditions. The adaptive turn-on detection circuit also enhances SR conduction efficiency during light load conditions, thereby improving the average efficiency of the power supply across the entire load range.

The synchronous switch can be configured at high-side or low-side output without auxiliary windings or other power sources, because the NEX81801/2DA has a self-supply capability.

The NEX81801/2DA uses TSOT23-6 packaging with low thermal resistance. This can effectively reduce the junction temperature of the chip, making it suitable for high-density power supply design.